Materials with a high, nonlinear dielectric constant have been found to be very beneficial when used for microelectronic applications in the radio frequency and/or microwave frequency regime. Materials that have been widely investigated for these applications include strontium titanate (SrTiO3), barium strontium titanate (BA1xe2x88x92xSrxTiO3 also referred to as BSTO), lead calcium titanate (Pb1xe2x88x92xCaxTiO3), and the like.
By far the most widely investigated materials for electrically tunable microwave devices are Ba1xe2x88x92xSrxTiO3. The operation temperature of the devices is largely determined by the ratio of Ba to Sr. These materials however exhibit a high dielectric loss which is undesirable for high performance microwave devices. For practical dc electrically tunable microwave devices (such as voltage tunable filters and phase shifters), it is desirable to have nonlinear dielectric materials that have as large a dielectric tunability and as low a dielectric loss as possible. The existing efforts to reduce the dielectric loss include adding dopants such as tungsten, manganese, and/or calcium into Ba1xe2x88x92xSrxTiO3. Other dopants have also been introduced into BSTO materials in an attempt to improve the material properties that are directly related to device performance. For example, U.S. Pat. Nos. 5,312,790, 5,427,988, 5,486,491, 5,635,433, 5,635,434, 5,693,429, 5,830,591 and 5,846,893 describe BSTO composites including additives or dopants such as magnesium oxide, aluminum oxide, zinc oxide, zirconium oxide, magnesium zirconate, magnesium aluminate, or magnesium titanate. Nevertheless, the existing approaches all suffer from the reduction of the dielectric constant and the dielectric tunability. In the latter case, the dielectric constant for these oxides is typically 10-20. The dielectric constant of solid solution Ba1xe2x88x92xSrxTiO3 varies due to composition and temperature, but is typically over 100. Therefore, depending upon the method of mixing and the quantity of dopant, the dielectric constant of composite materials is expected to decrease significantly.
A number of references have discussed altering the ratio of Ti to (Ba+Sr). For example, fin et al., Appi. Phys. Lett., vol. 76, no. 5, pp. 625-627 (2000) describe films with controlled compositions of Ti to (Ba+Sr) grown from a stoichiometric Ba0.5Sr0.55TiO3 target.
The common expectation of adding TiO2 to Ba1xe2x88x92xSrxTiO3 is that a single Ti-rich compound Ba1xe2x88x92xSrxTi1+yO3 phase will form. In contrast, the present inventors have now discovered that addition of TiO2 to Ba1xe2x88x92xSrxTiO3 can form a two phase composite material even under high temperature processing conditions. In other words, the resultant material maintains separated phases of TiO2 and Ba1xe2x88x92xSrxTiO3. This surprising observation led to the development of the present invention that shows many advantages compared to existing technologies.
One object of the present invention is to provide dielectric composite materials including two distinct material phases.
Another object of the present invention is to provide thin film dielectric composite materials including two distinct material phases.
A further object of this invention is to provide epitaxial and/or amorphous, polycrystalline, nanocrystalline thin film dielectric composite materials including two distinct material phases.
Yet another object of this invention is to provide dielectric composite materials having lower dielectric loss and adjustable dielectric tunability.
Yet another object of this invention is to provide dielectric composite materials having a low dielectric loss and an adjustable dielectric constant.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a dielectric composite material including at least two crystal phases of different components with TiO2 as a first component and a material selected from the group consisting of Ba1xe2x88x92xSrxTiO3 where x is from 0.3 to 0.7, Pb1xe2x88x92xCaxTiO3 where x is from 0.4 to 0.7, Sr1xe2x88x92xPbxTiO3 where x is from 0.2 to 0.4, Ba1xe2x88x92xCdxTiO3 where x is from 0.02 to 0.1, BaTi1xe2x88x92xZrxO3 where x is from 0.2 to 0.3, BaTi1xe2x88x92xSnxO3 where x is from 0.15 to 0.3, BaTi1xe2x88x92xHfxO3 where x is from 0.24 to 0.3, Pb1xe2x88x921.3xLaxTiO3+0.2x where x is 0.3, (BaTiO3)x(PbFe0.5Nb0.5O3)1xe2x88x92x where x is from 0.75 to 0.9, (PbTiO3)x(PbC0.5W0.5O3)1xe2x88x92x where x is from 0.1 to 0.45, (PbTiO3)x(PbMg0.5W0.5O3)1xe2x88x92x where x is from 0.2 to 0.4, and (PbTiO3)x(PbFe0.5Ta0.5O3)1xe2x88x92x where x is from 0 to 0.2, as the second component.
In another embodiment, the present invention provides a dielectric composite material including at least two crystal phases of different components, formed at high temperatures from TiO2 and a material selected from the group consisting of Ba1xe2x88x92xSrxTiO3 where x is from 0.3 to 0.7, Pb1xe2x88x92xCaxTiO3 where x is from 0.4 to 0.7, Sr1xe2x88x92xPbxTiO3 where x is from 0.2 to 0.4, Ba1xe2x88x92xCdxTiO3 where x is from 0.02 to 0.1, BaTi1xe2x88x92xZrxO3 where x is from 0.2 to 0.3, BaTi1xe2x88x92xSnxO3 where x is from 0.15 to 0.3, BaTi1xe2x88x92xHfxO3 where x is from 0.24 to 0.3, Pb1xe2x88x921.3xLaxTiO3+0.2x where x is from 0.23 to 0.3, (BaTiO3)x(PbFe0.5Nb0.5O3)1xe2x88x92x where x is from 0.75 to 0.9, (PbTiO3)x(PbCo0.5W0.5O3)1xe2x88x92x where x is from 0.1 to 0.45, (PbTiO3)x(PbMg0.5W0.5O3)1xe2x88x92x where x is from 0.2 to 0.4, and (PbTiO3)x(PbFe0.5Ta0.53)1xe2x88x92x where x is from 0 to 0.2.
The present invention also provides a process of forming a thin film dielectric composite material including at least two crystal phases of different components with TiO2 as a first component and a material selected from the group consisting of Ba1xe2x88x92xSrxTiO3 where x is from 0.3 to 0.7, Pb1xe2x88x92xCaxTiO3 where x is from 0.4 to 0.7, Sr1xe2x88x92xPbxTiO3 where x is from 0.2 to 0.4, Ba1xe2x88x92xCdxTiO3 where x is from 0.02 to 0.1, BaTi1xe2x88x92xZrxO3 where x is from 0.2 to 0.3, BaTi1xe2x88x92xSnxO3 where x is from 0.15 to 0.3, BaTi1xe2x88x92xHfxO3 where x is from 0.24 to 0.3, Pb1xe2x88x921.3xLaxTiO3+0.2xwhere x is from 0.23 to 0.3, (BaTiO3)x(PbFe0.5Nb0.5O3)1xe2x88x92x where x is from 0.75 to 0.9, (PbTiO3)x(PbCo0.5W0.5O3)1xe2x88x92x where x is from 0.1 to 0.45, (PbTiO3)x(PbMg0.5W0.5O3)1xe2x88x92x where x is from 0.2 to 0.4, and (PbTiO3)x(PbFe0.5Ta0.5O3)1xe2x88x92x where x is from 0 to 0.2, as the second component including the steps of forming a starting material including a mixture of TiO2 and the material selected from the group consisting of Ba1xe2x88x92xSrxTiO3, Pb1xe2x88x92xCaxTiO3, Sr1xe2x88x92xPbxTiO3, Ba1xe2x88x92xCdxTiO3, BaTi1xe2x88x92xZrxO3, BaTi1xe2x88x92xSnxO3, BaTi1xe2x88x92xHfxO3, Pb1xe2x88x921.3xLaxTiO3+0.2x, (BaTiO3)x(PbFe0.5Nb0.5O3)1xe2x88x92x, (PbTiO3)x(PbMg0.5W0.5O3)1xe2x88x92x, and (PbTiO3)x(PbFe0.5Ta0.5O3)1xe2x88x92x , depositing a thin film of the starting material on a substrate and heating the thin film of starting material for time and at temperatures sufficient to form said thin film dielectric composite material including at least two crystal phases of different components.